It is known to provide fluid sampling devices using optical near-field imaging. Such a device is employed to determine quantity, size, physical characteristics, and types of particulate matter in fluids. Examples of fluids which are monitored in such a system are lubricating oils used in engines and rotating machinery; hydraulic fluids used in equipment; and fluids used in industrial quality control, food processing, medical analysis, and environment control. In its most common use, such a device monitors engine oil for particulate debris, wherein a quantity, size, and shape of particulates correspond to an engine condition, and can alert one to particular problems with the engine. Predicting failure is critically important in aircraft engines to avoid accidents and loss of life.
The early stages of engine wear cause small particulate matter, of about 50 microns or less in size, to be generated. These particulates have characteristic shapes indicative of the type of wear produced by specific wear mechanisms. As the wear process progresses, the quantity and size of particulates increase. Accordingly, sensing and identifying smaller particles allows early identification of faults, thus, allowing more time for corrective maintenance and preventing unexpected catastrophic failures.
Although current devices such as the optical flow cell disclosed in U.S. Pat. No. 6,104,483, which is incorporated herein by reference, are sufficient in their stated purpose, such devices can be difficult to mass produce because they are manufactured using a potting process. For example, during the potting process, a viewing assembly along with an inlet tube and an outlet tube are positioned in a mold, and the mold is thereafter filled with a bonding material (i.e. epoxy resin).
The bonding material ultimately cures around the inlet tube, outlet tube, and viewing assembly to form the body of the optical flow cell. However, placement of the above-discussed components in the mold, and providing access to the viewing assembly is difficult. For example, the positioning of the inlet tube, outlet tube, and viewing assembly must be precisely accomplished. Therefore, considerable time is spent arranging the components in the mold, and insuring that the components are aligned as the bonding material fills the mold. Furthermore, to insure access through the body to the viewing assembly, various plungers or other inserts must be used to form a light entry aperture and an imaging aperture. The plungers or other inserts are positioned on either side of the viewing assembly prior to filling the mold with bonding material. The placement of the plungers or other inserts further complicates placement of the components in the mold, and the overall manufacture of the optical flow cell.
After the bonding material cures, a “potted” part is removed from the mold, and the plungers or other inserts, as well as extraneous epoxy resin are trimmed from the part. Thereafter, the part is cleaned, and additional epoxy is applied around the periphery of the light entry aperture to form a finished optical flow cell.
As can be appreciated, manufacture of such an optical flow cell is a time-consuming process. Moreover, precise positioning of the above-discussed components in the mold is difficult, thereby requiring additional skilled labor for assembly.
Therefore, there is a need for an optical flow cell which is relatively simple to manufacture. Such an optical flow cell should eliminate the need to use a potting process during manufacture, and be composed of pre-formed structural components. Such components should allow for manufacture of such an optical flow cell within small tolerances, and thereby provide for repeatable reference points.